Ccc v8 Carburetor Tests W/codes Cadillac Brougham I

MODEL IDENTIFICATION

Repair procedures in this article are sometimes identified by body type. The following table lists the General Motors division, model name, and body type.

MODEL IDENTIFICATION

Component Location (5.0L VIN Y, B & D Bodies. Scheme 37

Note. The following component locations refer to the locations identified in (Scheme 37).

Computer Harness

1. C1. Electronic Control Module (ECM)
2. C2. ALDL Diagnostic Connector
3. C3. "SERVICE ENGINE SOON" Light
4. C5. ECM Harness Ground
5. C6. Fuse Panel
6. C7. "SERVICE ENGINE SOON" Light Driver
7. C10. M/C Dwell Connector

Controlled Devices

1. 1. M/C Solenoid
2. 2. Idle Load Compensator
3. 5. Torque Converter Clutch (TCC) Connector
4. 6. Electronic Spark Timing (EST) Connector
5. 9. AIR Diverter Valve
6. 10. AIR Switching Valve
7. 12. EGR Vacuum Solenoid
8. 13. A/C Compressor Relay
9. 19 . Rear Vacuum Break Solenoid
10. 19a. Rear Vacuum Break
11. 20. ILC Solenoid
12. 21. Canister Purge Solenoid

Information Sensors

1. A. Oxygen (02) Sensor
2. B. Throttle Position Sensor
3. C. Coolant Temperature Sensor (CTS)
4. D. Vehicle Speed Sensor
5. E. ESC Module
6. F. Knock Sensor
7. G. Pressure Sensor

Emissions Systems (Not ECM Controlled)

1. N. PCV Valve
2. N2. EFE Valve
3. N16. Fuel Vapor Canister
4. N17. Fuel Vapor Canister
5. N18. Anti-Dieseling Solenoid
6. N20. Anti-Dieseling Vacum Tank

BASIC DIAGNOSTIC PROCEDURE

Note. Most engine control problems are the result of mechanical breakdowns, poor electrical connections or damaged vacuum hoses. Before considering the computer system as a possible cause of problems, ignition high tension wires, fuel supply, electrical connections and vacuum hoses should be checked. Failure to do so may result in lost diagnostic time.

Diagnosis of the computerized engine control system should be performed in the following order

1. Make sure that all engine systems not related to the computer system are operating properly. Do not proceed with testing unless all other problems have been repaired.
2. Perform appropriate DIAGNOSTIC CIRCUIT CHECK for that system. If codes were displayed (other than Code 12), decide whether they are "hard" or "intermittent" codes. "Hard" codes will cause the "SERVICE ENGINE SOON" light to illuminate continuously while engine is running. See «ECM TROUBLE CODE DEFINITION»(/cadillac/brougham/i-1987-1992/remont/testing-diagnostics/#ccc-v8-carburetor-tests-wcodes) table in this article.
3. If no trouble codes were displayed, proceed to appropriate SYSTEM PERFORMANCE CHECK.
4. If no trouble is indicated by the SYSTEM PERFORMANCE CHECK and/or a driveability problem exists, refer to SYMPTOM DIAGNOSIS in the CCC TESTS W/O CODES article in this section and/or the SCAN TESTER USAGE procedures in this article. The comments there will send you to the proper component charts or tell you the most likely system/component to check.
5. After any repairs are made, clear any trouble codes and perform SYSTEM PERFORMANCE CHECK or FIELD SERVICE MODE check.

Scheme 38

Scheme 39

1. Turn ignition on. Do not start engine. "SERVICE ENGINE SOON" light should glow. Locate Assembly Line Data Link (ALDL) connector attached to ECM wiring harness. For exact location of ALDL (Scheme 37) Insert jumper wire across terminal "B" (diagnostic "test" terminal), and terminal "A" (ground). (Scheme 39) CAUTION: Inserting spade lug (jumper lead) into terminals of ALDL connector grounds ALDL "test" terminal. Do not ground ALDL connector until after ignition is on (engine not running).
2. "SERVICE ENGINE SOON" light should flash Code 12. Code 12 consists of "FLASH", pause, "FLASH", "FLASH" followed by a longer pause. Code 12 will be repeated 2 more times. If any other trouble codes are stored in ECM memory, they will be displayed in the same manner.
3. To exit diagnostic mode, turn ignition off and remove jumper wire from ALDL connector.

READING TROUBLE CODES

The ECM stores component failure information for the CCC system under a related trouble code which can be recalled for diagnosis and repair. Trouble codes may be read by counting flashes of the "SERVICE ENGINE SOON" light, or by reading the output of a diagnostic "Scan" tester connected to the ALDL connector. The tester is faster, more accurate, and capable of reading information which otherwise would necessitate testing individual ECM and sensor/solenoid connector terminals with a digital voltmeter. See SCAN DATA TABLES and SCAN TESTER USAGE in this article.

If "Scan" tester is not available, it is possible to read flashes of the "SERVICE ENGINE SOON" light by grounding the diagnostic terminal of the ALDL with ignition on and engine off. For example, "FLASH", "FLASH", pause, "FLASH", longer pause, identifies Code 21. The first series of flashes are the first digit of trouble code. The second series of flashes are the second digit of trouble code. Trouble codes are displayed starting with the lowest numbered code. Each code is displayed 3 times. Codes will continue to repeat as long as ALDL "test" terminal is grounded.

Note. Trouble codes will be recorded at various operating times. Some codes require operation of that sensor or switch for 5 seconds; others may require operation for 5 minutes or longer at normal operating temperature, road speed and load. Therefore, some codes may not set in a service bay operational mode.

ECM TROUBLE CODE DEFINITIONS

ECM TROUBLE CODE DEFINITION

Note. Trouble code charts should only be used if "SERVICE ENGINE SOON" light is illuminated (indicating a current problem exists). Exceptions are Code 13, 15, 24, 44 and 45 charts, which may be used to help diagnose intermittent codes. Anytime Codes 51, 52, 54 or 55 are displayed with another code, start with "50-series" code first, then proceed to low profile numbered codes.

TROUBLE CODE DETERMINATION (HARD OR INTERMITTENT)

During any diagnostic procedure, it must be determined if codes are "hard" failure codes or "intermittent" failure codes. Diagnostic charts will not usually help analyze "intermittent" codes. To determine "hard" codes and "intermittent" codes, proceed as follows

1. MANUALLY enter diagnostic mode. Read and record all stored trouble codes. Exit diagnostic mode and clear trouble codes. See CLEARING TROUBLE CODES in this article.
2. Apply parking brake and place transmission in Neutral or Park. Block drive wheels and start engine. "SERVICE ENGINE SOON" light should go out. Run warm engine at specified curb idle for 2 minutes and note "SERVICE ENGINE SOON" light.
3. If "SERVICE ENGINE SOON" light comes on, MANUALLY enter diagnostic mode. Read and record trouble codes. This will reveal "hard failure" codes. Codes 13, 15, 24, 44, 45 and 55 may require a road test to reset "hard failure" after trouble codes were cleared.
4. If "SERVICE ENGINE SOON" light does not come on, all stored trouble codes were "intermittent failures". Exceptions are noted under DIAGNOSTIC PROCEDURE.

CLEARING TROUBLE CODES

Turn ignition switch to "ON" position and ground diagnostic terminal lead at ALDL connector. Turn ignition switch to "OFF" position and remove ECM fuse from fuse block for 10 seconds. Replace fuse. Remove diagnostic terminal ground lead.

DIAGNOSTIC MATERIALS

Note. The charts described in the following paragraphs are arranged later in this article, by engine size and fuel system type.

Diagnostic Charts

The diagnostic charts are used to find and repair problems which the on-car diagnostics have found. These charts include

1. Charts which test the reliability of the self-diagnostic system.
2. Charts which help fix problems which are "SERVICE ENGINE SOON" light related.
3. Charts which test the computerized fuel control system performance.
4. Charts which help fix a problem when the on-car diagnostics don't work.
5. ENGINE CRANKS BUT WON'T RUN charts.
6. Charts where a stored trouble code leads you to a particular problem. See ECM TROUBLE CODE DEFINITION and DIAGNOSTIC AIDS in this article.
7. Charts which are used because the SYSTEM PERFORMANCE CHECK (carbureted models) or FIELD SERVICE MODE CHECK (fuel injected models) found a problem.

Note. Although there are many charts connected with computer diagnosis, only 2 charts are needed to prove system is operating properly. Normally, only 3 charts are necessary to find a problem, if one exists.

Diagnostic Aids

Diagnostic aids (located in many "trouble code" charts) are additional tips used to help diagnose trouble codes when inspected circuit checks out okay. Diagnostic aids may help lead to a definitive solution to that trouble code problem.

System Performance Check (Carbureted Models)

This check verifies that computerized engine control system is functioning correctly. This check should always be made after any repair of computerized engine control system. Performance check chart can be found by proceeding to appropriate SYSTEM PERFORMANCE CHECK chart for that system type.

When performing this check, always engage parking brake and block DRIVE wheels. Parking brake on FWD models does NOT hold drive wheels.

Note. On some engines, oxygen sensor will cool off after only a short period of time while engine is idling. This will cause engine to go into "open loop". To restore "closed loop" mode, run engine at part throttle several minutes and accelerate from idle to part throttle several times.

Field Service Mode Check (Fuel Injected Models)

On fuel injected models, "SERVICE ENGINE SOON" light will indicate operational mode of engine if ALDL is grounded while engine is running. In "closed loop" mode, "SERVICE ENGINE SOON" light will flash at a rate of one flash per second. In "open loop", light will flash at a rate of 2.5 flashes per second. If light is off most of the time, a lean exhaust is indicated. If light is on most of the time, a rich exhaust is indicated.

This test confirms proper operation of fuel system and verifies "closed loop" operation. Clear codes and perform this test after any repair is completed. When performing this check, always engage parking brake and block DRIVE wheels. Parking brake on FWD models does NOT hold drive wheels.

Note. On some engines, oxygen sensor will cool off after only a short period of time while engine is idling. This will cause engine to go into "open loop". To restore "closed loop" mode, run engine at part throttle several minutes and accelerate from idle to part throttle several times.

SPECIAL TOOLS (DIAGNOSTIC)

Note. Special "Scan" testers plugged into the ALDL may be used to read trouble codes and check voltages in the system on the serial data line (terminal "D" on carbureted, terminal "E" on EFI and terminal "M" on EFI with P-4 systems). These testers can save a great deal of time. For additional information, see SCAN TESTER USAGE and SCAN TESTER DATA tables in this article.

The computerized engine control system is most easily diagnosed using a "Scan" tester, however, other tools may aid in diagnosing problems if a "Scan" tester is unavailable. These tools are a tachometer, dwell meter, test light, ohmmeter, digital voltmeter with 10-megohm input impedance (minimum), vacuum pump, vacuum gauge, fuel injector test lights (TBI and PFI) and 6 jumper wires 6" long (one wire with female connectors at both ends, one wire with male connector at both ends and 4 wires with male and female connectors at opposite ends). A test light, rather than a voltmeter, must be used when indicated by a diagnostic chart.

On carbureted models, a dwell meter can be used to measure the time M/C solenoid is on or off. Dwell reading indicates if M/C solenoid is working, as well as fuel mixture strength (rich or lean). The dwell meter is set on the 6-cylinder scale regardless of the number of cylinders in engine.

Dwell meter is connected to Green connector located near carburetor. This connector will not be connected to any circuit EXCEPT when testing with dwell meter. DO NOT allow terminal wire to come in contact with any ground source, including rubber hoses.

Note. If engine operation seems to change when dwell meter is connected to Green wire, remove dwell meter and use another type. Some models may not be compatible with computerized engine control system.

Before engine reaches operating temperature, dwell should be fixed between 10-50 degrees, indicating "open loop" operation. With engine at operating temperature and idling, dwell meter needle should be varying between 10-50 degrees. This indicates "closed loop" operation. If (after reaching normal operating temperature) dwell is fixed between 10-50 degrees, less than 10 degrees or more than 50 degrees, refer to appropriate CHART A - DWELL FIXED diagnostic chart for that system.

TERMINAL ID & PIN VOLTAGE CHARTS

The following conditions must be met before testing

1. Engine at operating temperature.
2. Engine in closed loop operation.
3. Engine idling ("Engine Run" column).
4. ALDL "test" terminal NOT grounded.
5. "Scan" tester NOT installed.

ECM Pin Voltage Chart (B & D Body). Scheme 40

DIAGNOSTIC CIRCUIT CHECK

The Diagnostic Circuit Check determines if the "SERVICE ENGINE SOON" light works, the ECM is operating and can recognize a fault and if any codes are stored.

This is the starting point for any diagnosis. If no codes are indicated, see SYSTEM PERFORMANCE CHECK. If no additional checks are called out from the System Performance Check, see TROUBLE SHOOTING and SCAN TESTER USAGE in the CCC TESTS W/O CODES article in this section.

Note. Test numbers refer to test numbers on diagnostic chart.

1. Check operation of "SERVICE ENGINE SOON" light. With key on, "Scan" tester not connected and engine not running, light should be on steady. "INTERMITTENTS" is located in CCC TESTS W/O CODES article in this section.
2. Grounding "test" terminal will flash a Code 12 and any stored trouble codes. The light must go completely off to indicate a code. If light goes from bright to dim, see CHART A6 - "SES" LIGHT ON, WON'T FLASH CODE 12. This is not considered a code.
3. See SCAN TESTER USAGE in the CCC TESTS W/O CODES article in this section. If "Scan" tester is not operating properly, try it on another vehicle. If it works on other vehicle, cigar lighter should be checked for battery voltage and a good ground. If "Scan" tester displays "NO DATA" or "NO ALDL" with ignition on, see CHART A6 - "SES" LIGHT ON, WON'T FLASH CODE 12.
4. No codes at this point indicate the problem is intermittent and SYSTEM PERFORMANCE CHECK should be performed. If one or more codes are displayed, see appropriate trouble code chart.

Diagnostic Circuit Check Schematic. Scheme 41

Diagnostic Circuit Check Flow Chart. Scheme 42

SYSTEM PERFORMANCE CHECK

Note. Test numbers refer to test numbers on diagnostic chart.

1. This test checks carburetor ability to change air/fuel mixture. Disconnecting M/C solenoid makes carburetor run full rich. Reconnecting it with dwell lead grounded makes carburetor run full lean. RPM normally drops 300-1000 RPM as solenoid is reconnected. A) If plugging PCV, purge, or bowl vent hose causes RPM to drop more than 300 RPM, plugged hose that caused 300 RPM or more drop leads to source of problem. If RPM increases as M/C solenoid is connected, this indicates system is running extremely rich. If no faults are found during system checks, service carburetor.
2. This test checks for proper control of idle circuit. A) Indicates "closed loop" operation. Normal dwell reading is 10-50 degrees but varying. Run engine at 2000 RPM for one minute to ensure O2 sensor is warm. B) This indicates an "open loop" condition that can be caused by one of the following: Open O2 sensor circuit or bad sensor; Open coolant sensor circuit; Open circuit No. 413, from ECM terminal No. 14 to ground. C) This indicates a full rich command to the carburetor, caused by one of the following: Lean engine condition; Grounded O2 sensor circuit No. 412 to ECM terminal No. 9, or bad sensor; Open circuit No. 413, from ECM terminal No. 14 to ground; Open circuit No. 452 to ECM terminal No. 22; Open in coolant sensor circuit No. 410 or No. 452. D) This indicates a full lean command which can be caused by one of the following: M/C solenoid wires reversed; Leaking bowl vent valve, excessive fuel in vapor canister, fuel in crankcase, faulty carburetor calibration or carburetor, or silicone contaminated O2 sensor.
3. Checks for proper control of main metering system. Engine speed must be at least 3000 RPM to get into the main metering system operation. A) A missing "O" ring between the switching valve solenoid and valve, or a defective valve, may cause air to leak into the exhaust ports at higher RPM only.

Note. SYMPTOMS is located in CCC TESTS W/O CODES article in this section.

System Performance Check Flow Chart. Scheme 43

CHART A1 - DWELL FIXED LESS THAN 10 DEGREES

Note. Test numbers refer to test numbers on diagnostic chart.

1. This test determines if problem is CCC or engine related. Dwell should start increasing as soon as engine is choked and increase until it is greater than 50 degrees. If dwell responds, problem is lean engine.
2. This test checks for ECM response to input to O2 sensor circuit. The voltmeter is used to put a voltage signal on the O2 sensor circuit to simulate a rich condition. Dwell should increase (lean command) if ECM and harness are good.
3. This test checks for normal coolant sensor circuit condition. Temperature on a normalized hot engine should be greater than 167°F (75°C).
4. This step checks for a circuit problem or high TPS input signal which could cause a full rich command.

Chart A1 Schematic, Dwell Fixed Less Than 10°. Scheme 44

Flow Chart A1, Dwell Fixed Less Than 10°. Scheme 45

CHART A2 - DWELL FIXED BETWEEN 10°-50°

Note. Test numbers refer to test numbers on diagnostic chart.

1. Grounding O2 sensor input checks ECM response to a "lean" signal. Normal response is dwell decreasing to full rich command.
2. This step grounds O2 sensor circuit at ECM to check for open in wiring to ECM terminal No. 9. Normal response to "lean" signal is a decrease in dwell.
3. This step checks coolant sensor input. Normal reading on a warm engine is greater than 167°F (75°C). An open circuit would cause a reading of approximately 77°F (25°C).
4. On some ECMs, an open circuit to terminal No. 14 can cause "open loop".
5. Checks output of O2 sensor with full rich command from ECM caused by grounding O2 sensor input circuit. Normal response is O2 sensor voltage reading greater than .8 volt.

Flow Chart A2, Dwell Fixed Between 10°-50°. Scheme 46

CHART A3 - DWELL FIXED GREATER THAN 50 DEGREES

Note. Test numbers refer to test numbers on diagnostic chart.

1. Determines whether problem is related to engine or electronics. Normal response is dwell decrease. This indicates that O2 sensor, harness and ECM are okay. Problem is a rich engine condition. If engine is very rich, a large air leak may be required to lean mixture. When mixture is lean enough, engine will begin to run rough.
2. Checks ECM response to a "lean" O2 signal. Normal response to this test is low dwell. No dwell change indicates a defective ECM. This test also eliminates the possibility of an open sensor wire. An open wire would cause "open loop" operation and may set Code 13.
3. Checks for excessive voltage in O2 line. If less than .55 volt, wire and ECM are okay. Fault is in O2 sensor. If greater than .55 volt, wire is shorted to battery voltage or ECM is faulty.
4. If plugging PCV or bowl vent vacuum hose causes dwell to decrease, that hose leads to source of problem. If no problems are found, service carburetor.

Flow Chart A3, Dwell Fixed Greater Than 50°. Scheme 47

CHART A5 - NO "SERVICE ENGINE SOON" LIGHT

Note. Test numbers refer to test numbers on diagnostic chart.

1. This checks for blown gauge fuse or open in "SERVICE ENGINE SOON" light circuit, including I.P. connector, printed circuit and "SERVICE ENGINE SOON" light. Normal response is light on.
2. This test checks for shorted ECM. A grounded ECM terminal "G" will turn "SERVICE ENGINE SOON" light off. If disconnecting ECM turns light on, ECM is shorted. Normal response is light on.
3. This test checks for grounded circuit No. 487 from terminal "C" of light driver to terminal "G" of ECM, an open circuit No. 439 to terminal "B" of light driver, bad ground or faulty light driver. Normal reading is 9-11 volts. If greater than 11 volts, a bad ground or a faulty light driver is indicated. Light driver is located in wiring harness near ECM.
4. This test checks for open in wire to terminal "B". Normal reading is about battery voltage. A) This test checks for an open circuit No. 439 to terminal "E" from "SERVICE ENGINE SOON" light. With terminal "E" grounded, normal response is light on. Light off indicates an open. Light on indicates a faulty light driver or light driver connection.
5. This test checks for a grounded circuit No. 487 from driver terminal "C" to ECM terminal "G". Normal response is light on.

Flow Chart A5, No "Service Engine Soon" Light. Scheme 48

CHART A6 - "SES" LIGHT ON, WON'T FLASH CODE 12

Note. Test numbers refer to test numbers on diagnostic chart.

1. This step checks for short to battery voltage in wire to terminal "C" or faulty light driver. Normal reading is 9-11 volts.
2. This step checks to see if problem is related to the ECM or light driver. Grounding terminal "C" should turn light off. If it does, problem is related to ECM and its wiring. If it does not, fault is related to light driver and its wiring. Light driver is located in wiring harness near ECM.
3. Grounding terminal "G" at ECM and finding light on indicates an open in circuit No. 487 to terminal "C" of light driver. Grounding terminal "G" should turn light off.
4. This step checks for open in circuit No. 451 from ECM to "test" terminal in ALDL connector. The light should flash Code 12 when terminal No. 5 is grounded.
5. This checks for proper voltage supply to ECM. Both should read greater than 9 volts. Terminal "C" is ignition and terminal "R" is constant battery voltage for long term memory.
6. This test checks for bad ground in ECM. Terminals "A" and "U" are connected together inside ECM.
7. This step distinguishes between a faulty ECM and PROM. Normal response is for Code 51 to flash even though PROM is not installed in ECM. If there is no Code 51, ECM is faulty.

Chart A6, "SES" Light Always On Or Won't Flash Code 12. Scheme 49

CHART B1 - RESTRICTED EXHAUST SYSTEM CHECK

Before any components are replaced, exhaust system must be checked for restrictions. Check at AIR pipe or check at O2 sensor procedure may be used to diagnose condition, depending on engine or tool used.

Check At Air Pipe

Remove rubber hose at exhaust manifold AIR pipe check valve and remove check valve. Install fuel pump pressure gauge to hose and nipple via Propane Enrichment Device (J26911 ) (Scheme 50) Nipple should be inserted into exhaust manifold AIR pipe.

Flow Chart B1, Checking For Restriction at AIR Pipe. Scheme 50

Check At O2 Sensor

Remove O2 sensor. Install backpressure tester in place of O2 sensor as shown in illustration. After test is completed, ensure that O2 sensor threads are coated with anti-seize compound before installation.

Flow Chart B1, Checking For Restriction at O2 Sensor. Scheme 51

Diagnosis

1. Start engine and bring to operating temperature. Increase engine speed to 2000 RPM and note gauge. Reading should not exceed 1.25 psi (.09 kg/cm 2 ).
2. If specification is exceeded, exhaust system restriction is indicated.
3. Check complete exhaust system for collapsed pipe, heat distress and possible internal muffler failure.
4. If none of these conditions exist, check for restricted catalytic converter. Replace if necessary.

CODE 12 - NO DISTRIBUTOR REFERENCE PULSES

This is a normal code with the ignition on and engine not running. With engine running, Code 12 could mean an open or ground in distributor reference circuit. Code 41 will appear with Code 12 if engine is running with no distributor reference signal. Code 41 will be stored even if problems clears.

Note. Test numbers refer to test numbers on diagnostic chart.

1. This test checks for a poor connection at EST connector as being the cause of no reference pulse. Terminal must be removed from connector and carefully inspected.
2. Voltage should normally be more than .5 volt, indicating that the signal is being generated by module and fault is a bad connection at ECM, or faulty ECM. To check ECM connection, terminal must be removed from connector.
3. If circuit No. 430 from terminal No. 10 to module is not open or grounded, source of no signal is the module.

Flow Chart & Schematic, Code 12, No Distributor Reference Pulses. Scheme 52

CODE 13 - OPEN OXYGEN SENSOR CIRCUIT

Note. Test numbers refer to test numbers on diagnostic chart.

1. This test checks to see if problem still exists. Code 13 indicates an open in the O2 sensor circuit under the following conditions: Engine at normal operating temperature. O2 sensor voltage is within a specified range (.35-.55 volt). Throttle angle greater than 6 percent (off idle). More than 40 seconds have elapsed since start-up.
2. Determines if sensor is at fault of wiring or ECM.
3. This test checks O2 sensor circuit wiring.

Flow Chart, Code 13, Open Oxygen Sensor Circuit. Scheme 53

CODE 14 - COOLANT TEMP SENSOR SIGNAL VOLT LOW

Note. Test numbers refer to test numbers on diagnostic chart.

1. Code 14 indicates the ECM has seen low coolant sensor voltage signal (high temperature) at ECM terminal No. 3 for 90 seconds or more.
2. This test checks for grounded circuit between ECM and coolant sensor.

After the engine is started, temperature should rise steadily to about 90°C (32°F), then stabilize when thermostat opens.

If the engine is allowed to cool overnight, coolant and MAT sensors should read close to each other when displayed on a "Scan" tester. When Code 14 is set, the ECM will turn on the cooling fan.

Flow Chart, Code 14, Coolant Temp Sensor Signal Volt Low. Scheme 54

CODE 15 - COOLANT TEMP SENSOR SIGNAL VOLTAGE HI

Note. Test numbers refer to test numbers on diagnostic chart.

1. Code 15 indicates that ECM has seen high resistance in coolant sensor circuit. This could be due to high resistance (cold engine temperature) or high voltage at ECM terminal No. 3 for 5 minutes or more after start.
2. This test simulates Code 14. If ECM recognizes the low voltage signal and sets Code 14, the ECM and wiring are not at fault.
3. This test determines if circuit No. 410 is open.

After the engine is started, temperature should rise steadily to about 90°C (32°F), then stabilize when thermostat opens.

If the engine is allowed to cool overnight, coolant and MAT sensors should read close to each other when displayed on a "Scan" tester.

Flow Chart, Code 15, Coolant Temp Sensor Signal Voltage High. Scheme 55

CODE 21 - TPS SIGNAL VOLTAGE HIGH

Code 21 indicates that ECM has seen a high Throttle Position Sensor (TPS) voltage for more than 10 seconds, less than a specified RPM (normally curb idle) or less than a specified engine load. Due to the pull-up resistor between terminals No. 21 and No. 2 within the ECM, an open in the TPS circuit will place about 5 volts (high TPS signal) at terminal No. 2 of ECM, resulting in a Code 21.

Note. Test numbers refer to test numbers on diagnostic chart.

1. This test checks circuit No. 417 and No. 452, from TPS connector back to ECM. Installing a jumper lead between harness terminals "B" and "C" should lower voltage at ECM terminal No. 2 to less than 2.5 volts.
2. Test light should be on if ground circuit No. 452 is okay.
3. If test light is on, circuit No. 417 could be open or ECM or connection at ECM could be faulty.

A "Scan" tester displays throttle position in volts. Closed throttle voltage should be less then .31-.41 volt with key on and engine off; however, the ECM "learns" and normalizes TPS reading so a voltage reading of .2-.7 volt is acceptable. Voltage should increase gradually to about 4.5 volts, at a steady rate, as throttle angle is increased.

Flow Chart, Code 21, TPS Signal Voltage High. Scheme 56

CODE 22 - THROTTLE POSITION SENSOR SIGNAL VOLTAGE LOW

Note. Test numbers refer to test numbers on diagnostic chart.

1. Code 22 indicates ECM has seen low Throttle Position Sensor (TPS) voltage (less than .2 volt) for longer than 20 seconds (with engine running).
2. Simulates Code 21. If ECM recognizes the high voltage signal, ECM and wiring are okay.

A "Scan" tester displays throttle position in volts. Closed throttle voltage should be less .31-.41 volt with key on and engine off; however, the ECM "learns" and normalizes TPS reading so a voltage reading of .2-.7 volt is acceptable. Voltage should increase gradually to about 4.5 volts, at a steady rate, as throttle angle is increased.

Flow Chart, Code 22, TPS Signal Voltage Low. Scheme 57

CODE 23 - M/C SOLENOID SIGNAL VOLTAGE LOW

Note. Test numbers refer to test numbers on diagnostic chart.

1. This test checks for a complete circuit from battery to M/C solenoid dwell lead. Normal reading should be battery voltage. Battery voltage means there might be an open circuit No. 411 between dwell connector and ground. No voltage could be caused by either an open between connector and ignition source or a ground on ECM side of M/C solenoid. If no problem is found, see INTERMITTENTS in the CCC TESTS W/O CODES article in this section.
2. This step checks for battery voltage on circuit No. 439 to ignition source. Test light should illuminate between ignition source and ground.
3. Determines whether fault is in M/C solenoid, a ground in ECM circuit No. 411, or ECM. A light will indicate a ground in circuit No. 411 to terminal No. 18 or a faulty ECM. A test light must be used in this step. A voltmeter may give an inaccurate indication.
4. This test checks for ground in circuit No. 411 to ECM terminal No. 18. If circuit is grounded, light will stay on.
5. Checks for open in circuit No. 411 from solenoid to ECM. Normal reading would be about battery voltage at terminal No. 18.
6. A normal solenoid will have about 20-32 ohms resistance. If M/C solenoid resistance is less than 10 ohms, the ECM does not have to be replaced because the ECM contains a fault protection Quad Driver in this circuit.

Code 23 Schematic, M/C Solenoid Signal Volt Low. Scheme 58

Flow Chart, Code 23, M/C Solenoid Signal Volt Low. Scheme 59

CODE 24 - VEHICLE SPEED SENSOR

The ECM applies and monitors 12 volts on circuit No. 437 to Vehicle Speed Sensor (VSS). VSS alternately opens and grounds circuit No. 437 when drive wheels are turning. This pulsing action takes place about 2000 times per mile and ECM calculates vehicle speed based on time between pulses. "Scan" tester reading should closely match speedometer reading.

Note. Test numbers refer to test numbers on diagnostic chart.

1. This test monitors ECM voltage on circuit No. 437. With drive wheels turning, pulsing action varies voltage. This variation is greater at low speeds to an average of 4-6 volts at about 20 MPH. Cruise control must be off for accurate test results.
2. A voltage of less than one volt indicates that circuit No. 437 is shorted to ground. Disconnect circuit No. 437 at VSS. The VSS is faulty if voltage now reads more than 10 volts. If voltage remains less than one volt, circuit No. 437 is grounded. If circuit is not grounded, check for a faulty ECM connector or ECM.
3. A steady 8-12 volts at ECM connector indicates circuit No. 437 is open, or a faulty VSS.
4. This is a normal voltage condition and indicates a possible intermittent condition. See INTERMITTENTS in the CCC TESTS W/O CODES article in this section.
5. This step will isolate whether problem is in circuit No. 437 or ECM.

Code 24 Schematic, Vehicle Speed Sensor. Scheme 60

Flow Chart, Code 24, Vehicle Speed Sensor. Scheme 61

CHART 24B - PARK/NEUTRAL CIRCUIT

The Park/Neutral (P/N) switch is closed when gear selector is in Park or Neutral and open in all other ranges.

Note. Test numbers refer to test numbers on diagnostic chart.

1. This step separates a faulty switch or switch adjustment from a faulty electrical circuit or ECM. Normal voltage across terminals of connector, when removed from P/N switch, should be approximately battery voltage.

Chart 24B Schematic, Park/Neutral. Scheme 62

Flow Chart 24B, Park/Neutral Circuit. Scheme 63

CODE 31 - CANISTER PURGE SOLENOID VOLT SIGNAL INCORRECT

Note. Test numbers refer to test numbers on diagnostic chart.

1. Canister purge solenoid should not be energized with ignition on and engine not running. Test light should be off. If light is on, either circuit No. 428 is shorted to ground or ECM is providing a ground, indicating a faulty ECM.
2. This step checks for battery voltage at the canister purge solenoid connector.
3. Grounding diagnostic "test" terminal at ALDL should energize solenoid, turning on test light if ECM and wiring are okay.
4. A low resistance solenoid will allow too much current to pass through ECM terminal No. 17. This will cause voltage at terminal No. 17 to be high even when commanded low by ECM.
5. Previous steps have verified that wiring and solenoid are okay. Faulty connections at the solenoid could cause an open circuit, resulting in Code 31. If connections are okay, condition is intermittent. See INTERMITTENTS in the CCC TESTS W/O CODES article in this section.

Solenoid coil resistance must measure more than 20 ohms. Less resistance will cause the canister purge driver to open within the ECM since the CCP Quad Driver is fault protected.

Code 31 Schematic, Canister Purge Solenoid Volt Signal Wrong. Scheme 64

Flow Chart, Code 31, Canister Purge Sol. Voltage Incorrect. Scheme 65

CODE 34 - PRESSURE SENSOR SIGNAL VOLTAGE INCORRECT

Code 34 indicates that ECM has seen manifold pressure outside a specified voltage range (seen by ECM as voltage at terminal No. 20), engine RPM less than a given value, engine at operating temperature and all conditions exist for a time greater than specified.

Note. Test numbers refer to test numbers on diagnostic chart.

1. An engine that is able to maintain 18 in. Hg of manifold vacuum will show about 4 volts on "Scan" tester.
2. If ECM and wiring are okay, "Scan" tester will show about .58 volt.
3. Low vacuum to sensor will show as low voltage on the "Scan" tester.
4. If circuit No. 452 is open, high voltage will show on the "Scan" tester.

Code 34 Schematic, Pressure Sensor Signal Volt Incorrect. Scheme 66

Flow Chart, Code 34, Pressure Sensor Signal Volt Incorrect. Scheme 67

CODE 41 - NO DISTRIBUTOR REFERENCE SIGNAL

Note. Test numbers refer to test numbers on diagnostic chart.

1. This test checks to see if pressure sensor voltage changes with loss of vacuum supply. When vacuum supply is lost, a properly functioning sensor will change voltage by one volt or more (measured from terminal "A" to "B" at sensor and terminal No. 20 to 22 at ECM).
2. This test checks for cause of an intermittent open or ground in distributor circuit. Fault could also be a pressure sensor that is intermittently stuck at the same voltage output as an engine running condition, with the ignition switch only in "ON" position. This condition will produce no reference signal. Terminals must be removed from connector to properly check them. The distributor pick-up coil should also be checked.
3. Since voltage change was less than one volt, problem is in pressure sensor system. The ECM has seen engine running vacuum equivalent with no distributor reference signal, with ignition on and engine not running. If Code 12 is present with engine running, a distributor reference fault is indicated and Code 12 chart should be referred to first. Also see Code 34 chart.

Flow Chart, Code 41, No Distributor Reference Signal. Scheme 68

CODE 42 - ELECTRONIC SPARK TIMING

Code 42 indicates that the ECM has seen an open or grounded by-pass circuit (terminal No. 11) or an open or grounded EST circuit (terminal No. 12). A grounded EST circuit may not set a code unless cranked 10 seconds or longer with circuit grounded.

Note. Test numbers refer to test numbers on diagnostic chart.

1. This test checks operation of EST. Grounding ALDL "test" terminal causes timing to go to a fixed value which is normally different from that obtained with EST operating, therefore, timing should change. Usually the change can be heard in engine RPM. If timing varies with increase in engine RPM (module advance), a problem is indicated.
2. This step eliminates the ECM and ECM connections from module input. By jumping terminals "A" and "B", the distributor reference signal is fed directly into the EST line of module. By putting voltage through the test light on harness terminal "C", the module is switched to EST mode and vehicle should run. If engine stops, there is no EST signal reaching the module due to open or poor connections, or module is faulty.
3. By removing the jumper, you are opening the EST signal, and engine should stop.
4. Since the engine ran when the module was jumpered, the problem is not in the distributor (if correct HEI module is installed). The wrong HEI module can set a Code 42.

Possible causes for intermittent Code 42 include loose grounds or electrical connections, extended cranking time (over 10 seconds with fully charged battery), abrupt recycling of ignition switch from "ON" to "OFF" position and back on again (within 5 seconds) or EST harness routed close to plug wires or other high load electrical harness.

Flow Chart & Schematic, Code 42, Electronic Spark Timing. Scheme 69

CODE 43 - ELECTRONIC SPARK CONTROL SIGNAL VOLTAGE LOW

Note. Test numbers refer to test numbers on diagnostic chart.

1. If knock retard is reading high, the ECM is monitoring a low voltage signal on circuit No. 457 at ECM terminal "L".
2. Probing ESC harness terminal "C" with a test light to battery voltage should result in a low knock retard signal.
3. If more than 6 volts is measured at ECM terminal "L", circuit No. 457 is okay and the fault is due to a poor ECM connection or a faulty ECM.

Check for poor connections or damaged harness. Inspect ECM harness connectors for backed out terminal "L", improper mating, broken locks, improperly formed or damaged terminals or damaged harness. If connections and harness check out okay, monitor knock signal parameter using "Scan" tester while moving related connectors and wiring harness. If failure is induced, knock signal will abruptly change. This may help to isolate the malfunction.

Flow Chart & Schematic, Code 43, ESC Signal Volt Low. Scheme 70

CODE 44 - LEAN EXHAUST INDICATION

Note. Test numbers refer to test numbers on diagnostic chart.

1. System will return to "open loop" if O2 sensor cools off while engine is idling. Scan "loop" status often during testing. For intermittent condition, see INTERMITTENTS in the CCC TESTS W/O CODES article in this section.
2. Checks if ECM is able to respond to a rich condition caused by choking the engine. If ECM responds, problem is a lean engine condition, NOT ELECTRICAL.
3. This step puts a rich O2 signal (about one volt) into terminal No. 9 of ECM. Dwell should increase (lean command).
4. If dwell increases to greater than 50 degrees with heavy choking, fault is an air leak, since ECM was able to respond. If air is going to exhaust ports, disconnect solenoid(s) for the air control valve. If air still goes to ports, valve is faulty. Repair exhaust leaks as necessary. If no exhaust leaks are found, service carburetor.

Flow Chart, Code 44, Lean Exhaust Indication. Scheme 71

CODE 45 - RICH EXHAUST INDICATION

Note. Test numbers refer to test numbers on diagnostic chart.

1. System will return to "open loop" if O2 sensor cools off while engine is idling. Scan "loop" status often during testing. For intermittent condition, see INTERMITTENTS in the CCC TESTS W/O CODES article in this section.
2. This step causes a lean condition by putting an air leak into engine to see if ECM can respond. A drop in dwell indicates that ECM and O2 sensor are not faulty. Look for source of constant rich condition. See DIAGNOSTIC AIDS below.
3. This step tests ECM response to a lean O2 signal (low voltage). If there is no dwell change with a grounded lead to O2 sensor terminal No. 9, fault is in ECM. Open O2 sensor circuit would have set Code 13.
4. The system's response in step 2) indicates the exhaust is actually rich. This could be due to a reverse connected M/C solenoid or excessive fuel in the engine. If all checks are okay, service carburetor.

Engine should be checked for cause of intermittent rich condition. Check for purge or bowl vent valves leaking, fuel in crankcase, fuel in evaporative canister, or sticking mixture control solenoid or metering rods. If Code 45 is intermittent, see INTERMITTENTS in the CCC TESTS W/O CODES article in this section.

Flow Chart, Code 45, Rich Exhaust Indication. Scheme 72

CODE 51 - PROM

Code 51 sets in the event of a faulty PROM unit, if PROM unit improperly installed (may not set a code if installed backward) or if some PROM pins not making contact (i.e. bent). Ensure PROM pins are not bent and are inserted properly into ECM. Ensure PROM is installed in proper direction as shown in chart.

CODE 53 - EGR SYSTEM MALFUNCTION (CALIF ONLY)

Note. Test numbers refer to test numbers on diagnostic chart. Steps 1-3 represent an EGR system operational check.

1. This test checks to see if the EGR passages are restricted or if valve is stuck open. Engine should run roughly or stall as valve is opened manually.
2. EGR valve diaphragm should begin to move as engine speed approaches 2000 RPM.
3. This test should result in EGR solenoid being energized, shutting off vacuum to EGR valve. This indicates system is functioning properly.
4. If vacuum is less than 7 in. Hg at 2000 RPM, a leak or restriction between the EGR diaphragm and vacuum source is indicated.
5. With ignition on and engine stopped, ECM normally grounds terminal "T" to energize the EGR solenoid. This test checks EGR solenoid and solenoid electrical control circuit.
6. The EGR is normally de energized with the engine idling at normal operating temperature. This test checks EGR solenoid and solenoid electrical control circuit.
7. This determines whether ECM is providing ground to terminal "T" or circuit No. 435 is shorted to ground.

Vacuum hoses should be checked for internal restrictions. The ECM uses the pressure sensor for checking EGR operation. If there is a question of pressure sensor accuracy, see component CHART C1D. If no problems are found, see INTERMITTENTS in the CCC TESTS W/O CODES article in this section.

Code 53 Schematic, EGR System Malfunction (Calif.). Scheme 73

Flow Chart, Code 53, EGR System Malfunction (Calif.). Scheme 74

CODE 54 - M/C SOLENOID SIGNAL VOLTAGE HIGH

Note. Test numbers refer to test numbers on diagnostic chart.

1. This test checks the M/C solenoid resistance to determine if fault is in the solenoid, ECM harness or ECM. Normal resistance reading for a solenoid is 20-32 ohms. Since the ECM is protected by a fault protection Quad Driver, if M/C solenoid resistance is less than 10 ohms, only solenoid need be replaced, not the ECM.
2. Checks if reason for high voltage to terminal No. 18 is a faulty ECM or a short to 12 volts in circuit No. 411. If test light to ground lights at M/C solenoid test lead with both ends of harness disconnected, there is a short to 12 volts in circuit No. 411.

Flow Chart/Schematic, Code 54, M/C Sol. Signal Voltage High. Scheme 75

CHART C1D - PRESSURE SENSOR

Note. Test numbers refer to test numbers on diagnostic chart.

1. With ignition on and engine not running, the pressure sensor functions as a BARO sensor.
2. If pressure sensor wiring and ECM are okay, the voltage will drop, simulating a change in altitude. If wiring is open or shorted to ground, "Scan" tester reading will always stay high.

Chart C1D Schematic, Pressure Sensor. Scheme 76

Flow Chart C1D, Pressure Sensor. Scheme 77

CHART C2C - IDLE LOAD COMPENSATOR

Note. Test numbers refer to test numbers on diagnostic chart.

1. ILC should be extended as no vacuum is applied.
2. ILC should retract if vacuum is applied.
3. Depressing the TPS simulates a WOT signal. This should make the ECM turn the ILC Quad Driver on, blocking vacuum to the ILC. Clear long term memory after this procedure. ECM will need to "relearn" correct TPS adjustment.
4. With "test" terminal grounded and TPS depressed, ECM should be turning on ILC solenoid. Test light should be on.
5. Anti-dieseling solenoid is energized anytime ignition is on, so test light should be on.
6. Test light should be off, as ILC Quad Driver should be turned off.
7. If test light goes out, ECM has to be replaced due to a faulty Quad Driver.

Chart C2C Schematic, Idle Load Compensator. Scheme 78

Flow Chart C2C, Idle Load Compensator (1 Of 2). Scheme 79

Flow Chart C2C, Idle Load Compensator (2 Of 2). Scheme 80

CHART C2D - REAR VACUUM BREAK

Note. Test numbers refer to test numbers on diagnostic chart.

1. This checks for normal RVB operation. With engine at normal operating temperature, RVB plunger should retract and pull the choke valve open.
2. This step simulates a cold engine by disconnecting the CTS. After sensor is disconnected, ignition must be cycled for each 30 seconds of RVB action.
3. Checks to see if retracted RVB from step 1) was due to no electrical signal to energize RVB solenoid, or a faulty solenoid. Solenoid should be energized with the ignition on and engine stopped. Test light should be on in step if electrical circuit is okay.
4. This step separates an electrical short from a vacuum problem. By de energizing the solenoid, the RVB should normally retract.
5. If test light goes off, ECM Quad Driver within ECM is faulty. Replace ECM.

Chart C2D Schematic, Rear Vacuum Break. Scheme 81

Flow Chart C2D, Rear Vacuum Break. Scheme 82

CHART C2F - TPS ENRICHMENT CHECK

Note. Test numbers refer to test numbers on diagnostic chart.

1. TPS idle service specification is .2-.7 volt.
2. "Scan" tester indicates actual TPS signal voltage received by ECM. If voltage drops low at any point while opening throttle, ensure it is not due to movement of the harness causing an intermittent. "Scan" tester only updates information from TPS each 1.25 seconds, so it may be necessary to backprobe ECM terminal No. 23 with a DVOM to locate an intermittent problem.
3. Adjust TPS to specification. If TPS can not be adjusted, replace TPS.
4. The 510,000-ohm resistor inside the ECM should cause the TPS signal to be high when the TPS is disconnected, unless circuit No. 417 is shorted to ground or ECM is faulty.
5. This step distinguishes between a faulty TPS and a circuit problem causing loss of 5-volt reference to TPS.
6. The 510,000-ohm resistor inside the ECM should cause the TPS signal to have 5 volts if the TPS is disconnected, unless circuit No. 417 is shorted to ground or the ECM is faulty. If ECM is putting 5 volts on circuit No. 417 but does not indicate an over 4.50 volt TPS signal on "Scan" tester, the ECM is faulty.

Chart C2F Schematic, TPS Enrichment Check. Scheme 83

Flow Chart C2F, TPS Enrichment Check. Scheme 84

CHART C3 - CANISTER PURGE SOLENOID

Note. Test numbers refer to test numbers on diagnostic chart.

1. Checks to see if solenoid is open or closed. Solenoid is normally de energized in this step so it should be closed.
2. Completes functional check. This should normally energize solenoid and allow vacuum to drop (purge "on").
3. Checks for open or shorted solenoid circuit.
4. Checks to see if ECM control circuit or solenoid is at fault. Solenoid coil resistance must measure more than 20 ohms. Less resistance will cause the canister purge driver inside ECM to open since Quad Drivers are fault protected.
5. If test light goes off with ECM disconnected, Quad Driver within the ECM is faulty. Replace ECM.

Flow Chart & Schematic, C3, Canister Purge Solenoid. Scheme 85

CHART C4A - IGNITION SYSTEM CHECK

Note. Test numbers refer to test numbers on diagnostic chart.

1. This tests for proper output from ignition system. Using Spark Tester (ST-125 ), check for spark at plugs. Tester requires a minimum of 25,000 volts to fire. This test can be used in case of an ignition misfire because system may provide enough voltage to run the engine, but not enough to fire spark plug under load. A) If spark occurs with EST connector disconnected, pick-up coil output is too low for EST operation.
2. Normal reading during cranking is about 8-10 volts.
3. This tests for a shorted module or grounded circuit from ignition coil to module. The distributor module should be turned off so that normal voltage should be about 12 volts. If module is turned on, voltage would be low but greater than one volt. This could cause the ignition coil to fail from excessive heat. With an open ignition coil primary winding, a small amount of voltage will leak through the module from "BAT" terminal to "TACH" terminal.
4. This checks voltage output with pick-up coil triggering module. A spark indicates ignition system has enough output. An intermittent no start or poor performance can result if polarity of ignition coil and pick-up coil is not correct. The color of the pick-up coil connector has to be Yellow if one of the ignition coil leads is Yellow. If ignition coil has a White lead, any pick-up coil connector color EXCEPT Yellow is okay.
5. This tests for an open module or module circuit. Applying 12 volts to terminal "P" of module should turn module on and voltage should drop to about 7-9 volts.
6. This should turn off module and cause a spark. If no spark occurs, fault is most likely in ignition coil, not module. A module tester could determine which is at fault.

Chart C4A Schematic, Ignition System Check. Scheme 86

Flow Chart C4A, Ignition System Check. Scheme 87

CHART C4K - ELECTRONIC SPARK TIMING PERFORMANCE CHECK

Note. Test numbers refer to test numbers on diagnostic chart.

1. Grounding ALDL "test" terminal causes system to go to a fixed spark advance, which should be different from that obtained with EST operating. Engine is run at fast idle to get more spark advance. Usually, the change in timing is enough so it can be heard as a change in RPM. If so, it is not necessary to check ignition timing.
2. Check timing change with vehicle in Drive. Some engines do not have EST operation in Park/Neutral.
3. This test checks if fault is in pressure sensor system.

Flow Chart & Schematic C4K, EST Performance Check. Scheme 88

CHART C5 - ELECTRONIC SPARK CONTROL

Note. Test numbers refer to test numbers on diagnostic chart.

1. This is an ESC functional test. Simulating engine knock by tapping on the engine block should cause a drop in RPM (decrease in timing). If RPM doesn't drop, either timing is not retarding or is retarded all the time.
2. This should cause the timing to fully retard by dropping voltage at the ECM terminal "L". Retarding timing should cause the RPM to drop.
3. Normally voltage should be .08 volt AC, or more for a good knock sensor circuit.
4. "SERVICE ENGINE SOON" light should be on and a Code 43 set because ESC system was retarded too long. If no light comes on, ECM is not retarding the spark because of voltage present on circuit No. 457 to terminal "L" or ECM is faulty.
5. This tests if knock sensor is reason for retard signal. If engine knock is not present and timing increases when knock sensor is disconnected, faulty knock sensor is the cause.
6. This tests if retard signal is due to "noise" on signal wire or a faulty controller. If timing increases when wire is disconnected from controller, fault is due to knock sensor signal wire running too close to an ignition or charging system wire. Reroute wire to correct.

Flow Chart & Schematic C5, Electronic Spark Control. Scheme 89

CHART C6A - AIR MANAGEMENT CHECK

Air management is controlled by electric air divert and air switching valves, each with an ECM controlled vacuum solenoid. When solenoid is grounded by ECM, manifold vacuum will activate valve and allow air pump air to be directed as follows

1. Air control (divert) solenoid not grounded by ECM - Air pump air is diverted.
2. Air control (divert) solenoid grounded by ECM - Air pump air to air switching valve.
3. Air switching solenoid not grounded by ECM - Air pump air to converter.
4. Air switching solenoid grounded by ECM - Air pump air to exhaust ports.

Loss of vacuum would cause air to be diverted to air cleaner.

Note. Test numbers refer to test numbers on diagnostic chart.

1. Air is directed to exhaust ports during "open loop" and engine starting. Engine always starts in "open loop", even on a warm engine. Since the air to exhaust ports time is very short, prepare to observe port delivery prior to start of engine.
2. This should set a Code 23. When any code is set, ECM opens ground circuit No. 429 to air diverter valve. This checks ECM response to a fault. A ground in diverter valve circuit No. 436 to ECM would prevent diverter valve action.
3. This test checks for a grounded circuit No. 429 to ECM. Test light off is normal and indicates circuit is not grounded.
4. This test checks for an open in solenoid control circuits. Grounding ALDL "test" terminal should ground both solenoid circuits. Normally, test light should be on, which indicates problem is not in ECM or wiring. Problem is in solenoid valve or connections.
5. Checks for a grounded switching valve circuit No. 436. Test light off indicates circuit is okay and fault is in valve.
6. If test light goes off, the Quad Driver within ECM is faulty and ECM must be replaced.

Chart C6A Schematic, Air Management Check. Scheme 90

Flow Chart C6A, Air Management Check. Scheme 91

CHART C7C - EGR CHECK

Note. Test numbers refer to test numbers on diagnostic chart. Steps 1-3 represent an EGR functional check.

1. This test checks to see if the EGR passages are restricted or if valve is stuck open. Engine should run roughly or stall as valve is opened manually.
2. EGR valve diaphragm should begin to move as engine speed approaches 2000 RPM.
3. This test should result in EGR solenoid being energized, shutting off vacuum to EGR valve. This indicates system is functioning properly.
4. If vacuum is less than 7 in. Hg at 2000 RPM, a leak or restriction between the EGR diaphragm and vacuum source is indicated.
5. With ignition on and engine stopped, ECM normally grounds terminal "T" to energize the EGR solenoid. This test checks EGR solenoid and solenoid electrical control circuit.
6. The EGR is normally de energized with the engine idling at normal operating temperature. This test checks EGR solenoid and solenoid electrical control circuit.
7. This determines whether ECM is providing ground to terminal "T" or circuit No. 435 is shorted to ground.

Vacuum hoses should be checked for internal restrictions.

Chart C7C Schematic, EGR Check. Scheme 92

Flow Chart C7C, EGR Check. Scheme 93

CHART C8 - TORQUE CONVERTER CLUTCH ELECT DIAGNOSIS

Note. Test numbers refer to test numbers on diagnostic chart.

1. This test confirms a 12-volt supply as well as continuity of TCC circuit.
2. When ALDL "test" terminal is grounded with engine off, ECM capability is energized to control the solenoid.
3. Test light should go off if circuit is okay because grounding terminal "P" shorts out test light. If test light goes off, ECM is faulty.
4. If test light goes off, the Quad Driver inside the ECM is faulty. ECM must be replaced.
5. Solenoid coil resistance must measure more than 20 ohms. Less resistance will cause continual opening of ECM Quad Driver. Using an ohmmeter, check solenoid coil resistance of all ECM-controlled solenoids and relays. Replace any solenoid or relay that measures less than 20 ohms.

An engine coolant thermostat that is stuck open or opens at too low a temperature may result in an inoperative TCC. On 200-4R transmission, if TCC engages before "Scan" tester indicates TCC "ON", wiring may be grounded between TCC solenoid and sump over temperature switch or switch may be faulty.

Chart C8 Schematic, TCC Electrical Diagnosis. Scheme 94

Flow Chart C8, TCC Electrical Diagnosis. Scheme 95

CHART C9C - VACUUM ACTUATED EFE SYSTEM CHECK (NON-CEC)

Note. Test numbers refer to test numbers on diagnostic chart.

1. Engine coolant temperature should be less than 73°F (23°C).
2. There should be at least 10 in. Hg (34 kPa) vacuum available to EFE actuator diaphragm.
3. Valve may be seized. It may be freed using Heat Valve Lubricant (1052627). If valve does not free, replace valve.
4. EFE valve should be open when temperature is greater than 90°F (32°C).
5. Vacuum at actuator on a warm engine indicates a faulty TVS. If no vacuum is present and actuator does not move, actuator and valve should be replaced.

Flow Chart/Schematic C9C, Vacuum EFE System (Non-CEC). Scheme 96

CHART C10C - A/C CUT-OUT RELAY

The A/C cut-out relay is a normally closed relay. The ECM opens the relay by providing a ground on circuit No. 449. This occurs during wide open throttle, an overheat condition, and momentarily during engine start-up on a warm engine.

Note. Test numbers refer to test numbers on diagnostic chart.

1. The A/C system must be fully charged so that the pressure cycling switch contacts are closed.
2. If ECM monitors Wide Open Throttle (WOT) simulated by fully depressing the TPS plunger, the A/C cut-out relay Quad Driver in the ECM is turned on, energizing the relay. This will cause current interruption to A/C clutch. Anytime TPS is fully depressed, long term ECM memory must be cleared to allow resetting of the TPS auto ranging feature.
3. Grounding the ALDL "test" terminal should turn on the A/C cut-out relay and Quad Driver in the ECM, allowing current to flow through the test light.
4. Test determines if relay is at fault or ECM circuit operation is incorrect.
5. If the test light is on, the circuit is either grounded or ECM Quad Driver is on. The ECM will have to be replaced if the test light goes off when ECM connector is disconnected because the Quad Driver in the ECM is faulty.

Flow Chart & Schematic C10C, A/C Cut-Out Relay. Scheme 97

Wiring Diagram (D Body). Scheme 98

Wiring Diagram (B Body). Scheme 99

See also:
• ECM TROUBLE CODE DEFINITION